This invention relates to a heat transfer method for controlling the temperature of warm-formed workpieces. More particularly, this invention relates to a method for thermally conditioning such workpieces.
Warm forming of workpieces is a process frequently encountered in the manufacturing industry. With such process, metal billets or slugs are preheated to a desired preheat temperature from their normal ambient air temperature of about 70.degree. F. and placed in, for example, a forming press. The press mechanically works the slug into a desired workpiece shape or form. By preheating the workpiece, flow of the metal in the forming process is facilitated. The mechanical working of the preheated slug into the workpiece form raises the temperature significantly (approximately 200.degree. F.). For example, after warm forming, the metal workpiece may achieve a temperature of 1,300.degree. F. After leaving the forming press, it is desirable to have a cooling in air to below the Martensite temperature of about 1,200.degree. F. This slow cooling is desirable in order to ensure proper grain formation in the formed part or workpiece. This is followed by a water quench to take the workpiece back to ambient temperature at which it may be easily handled.
Currently, temperature-conditioning apparatus and methods in use with warm-forming operations are unduly costly in terms of space and energy. With regard to space, current processes require numerous pieces of equipment for heating the slug, transferring it to the forming press, then cooling and quenching the formed workpiece. Numerous mechanical transfer stations are required for transferring the slug and formed workpiece. Typically, a straight-line orientation of transfer from process to process is required.
With respect to energy, heat is first added to the slug from an outside source such as an induction heat in the preheating operation. Mechanical working of the slug causes additional heating of the part. Then, a slow cooling process is imposed and the heat energy taken from the formed workpiece is essentially wasted. Further, prior quenching processes involve a direct quench whereby the workpiece is dropped into a bath of cold water. This bath quench is overly severe in that it takes the temperature of the workpiece down in step-wise fashion as opposed to a more desirable gradual quench.